Waste Silicon Being Reused in Flexible Lithium-Ion Batteries

Clean technologies like solar cells and lithium-ion batteries allow us to use renewable energy and use energy more efficiently, but often the materials that they're made from are scarce, expensive, hard to recycle or all of the above. Many researchers have been trying to tackle this problem by either developing technologies that uses more abundant materials, like these solar cells, or by finding ways to reuse and recycle the materials already being used in advanced technologies.

A partnership between Rice University and the Université catholique de Louvain in Belgium is focusing on the latter. The researchers have found a way to use waste silicon that would otherwise be discarded to make flexible lithium-ion batteries that could actually store more energy and be a step toward batteries that can conform to any shape and cost less to make.

Rice University reports, "The Rice lab of materials scientist Pulickel Ajayan created forests of nanowires from high-value but hard-to-recycle silicon. Silicon absorbs 10 times more lithium than the carbon commonly used in LI batteries, but because it expands and contracts as it charges and discharges, it breaks down quickly.

The Ajayan lab reports this week in the journal Proceedings of the National Academy of Science on its technique to make carefully arrayed nanowires encased in electrically conducting copper and ion-conducting polymer electrolyte into an anode. The material gives nanowires the space to grow and shrink as needed, which prolongs their usefulness. The electrolyte also serves as an efficient spacer between the anode and cathode."

For this waste silicon battery to actually make it into our devices one day, the researchers knew that the manufacturing process had to be simple to replicate and scalable. They used the established processes of colloidal nanosphere lithography to create an anti-corrosion barrier on the silicon and metal-assisted chemical etching to create millions of nanowires out of a silicon wafer. An electrolyte was then used to create a flexible matrix out of the nanowires that can easily be peeled off the wafer and then used in a lithium-ion battery. The researchers say that these processes can easily be done with silicon wafers the size of pizzas.

The resulting battery using the silicon nanowire array was able to put out 150 milliamp hours per gram. Even after 50 charge and recharge cycles, the battery showed little signs of decay. The researchers are now working on improving those figures and testing different battery configurations.